In humans, the heart beats to sustain life. In normal operation, it pumps blood through the various parts of the body. More particularly, the various chamber of the heart contract and expand in a periodic and coordinated fashion, which causes the blood to be pumped regularly. More specifically, the right atrium sends deoxygenated blood into the right ventricle. The right ventricle pumps the blood to the lungs, where it becomes oxygenated, and from where it returns to the left atrium. The left atrium pumps the oxygenated blood to the left ventricle. The left ventricle, then, expels the blood, forcing it to circulate to the various parts of the body and from where it returns to the right atrium to start the oxygenation-deoxygenation cycle of the blood all over again.
The heart chambers pump because of the heart's electrical control system. More particularly, the sinoatrial (SA) node generates an electrical impulse, which generates further electrical signals. These further signals cause the above-described contractions of the various chambers in the heart to occur in the correct sequence. The electrical pattern created by the sinoatrial (SA) node is called a sinus rhythm.
Sometimes, however, the electrical control system of the heart malfunctions, which can cause the heart to beat irregularly, or not at all. The cardiac rhythm is then generally called an arrhythmia. Arrhythmias may be caused by electrical activity from locations in the heart other than the SA node. Some types of arrhythmia may result in inadequate blood flow, thus reducing the amount of blood pumped to the various parts of the body. Some arrhythmias may even result in a Sudden Cardiac Arrest (SCA). In an SCA, the heart fails to pump blood effectively, and, if not corrected, can result in death. It is estimated that SCA results in more than 250,000 deaths per year in the United States alone. Further, an SCA may result from a condition other than an arrhythmia.
One type of arrhythmia associated with SCA is known as Ventricular Fibrillation (VF). VF is a type of malfunction where the ventricles make rapid, uncoordinated movements, instead of the normal contractions. When that happens, the heart does not pump enough blood to deliver enough oxygen to the vital organs. The person's condition will deteriorate rapidly and, if not corrected in time, will result in death, e.g. within ten minutes.
Ventricular Fibrillation can often be reversed using a life-saving device called a defibrillator. A defibrillator, if applied properly, can administer an electrical shock to the heart. The shock may terminate the VF, thus giving the heart the opportunity to resume normal contractions in pumping blood. If VF is not terminated, the shock may be repeated, often at escalating energies.
A challenge with defibrillation is that the electrical shock must be administered very soon after the onset of VF. There is not much time to do this since the survival rate of persons suffering from VF decreases by about 10% for each minute the administration of a defibrillation shock is delayed. After about 10 minutes the rate of survival for SCA victims averages less than 2%.
The challenge of defibrillating early after the onset of VF is being met in a number of ways. First, for some people who are considered to be at a higher risk of VF or other heart arrythmias, an Implantable Cardioverter Defibrillator (ICD) can be implanted surgically. An ICD can monitor the person's heart, and administer an electrical shock as needed. As such, an ICD reduces the need to have the higher-risk person be monitored constantly by medical personnel.
Regardless, VF can occur unpredictably, even to a person who is not considered at risk. As such, VF can be experienced by many people who lack the benefit of ICD therapy. When VF occurs to a person who does not have an ICD, they collapse, because the blood flow has stopped. They should receive therapy quickly after the onset of VF or they will die.
For a VF victim without an ICD, a different type of defibrillator can be used, which is called an external defibrillator. External defibrillators have been made portable, so they can be brought to a potential VF victim quickly enough to revive them.
During VF, the person's condition deteriorates because the blood is not flowing to the brain, heart, lungs, and other organs. The blood flow must be restored, if resuscitation attempts are to be successful.
Cardiopulmonary Resuscitation (CPR) is one method of forcing blood to again flow in a person experiencing cardiac arrest. In addition, CPR is the primary recommended treatment for some patients with some kinds of non-VF cardiac arrest, such as asystole and pulseless electrical activity (PEA). CPR is a combination of techniques that include chest compressions to force blood circulation, and rescue breathing to force respiration.
Properly administered CPR provides oxygenated blood to critical organs of a person in cardiac arrest, thereby minimizing the deterioration that would otherwise occur. As such, CPR can be beneficial for persons experiencing VF, because it slows down the deterioration that would otherwise occur while a defibrillator is being retrieved. For patients with an extended down-time, survival rates are higher if CPR is administered prior to defibrillation.
One common challenge for both automated and manual rhythm assessment in connection with defibrillation is that the high level of charges applied to a therapy electrode of a defibrillator for the purpose of “shocking” the heart may electrically interfere with the low level charge electrical signals that are generated by a monitoring electrode that may be used with the defibrillator for the purpose of monitoring the patient throughout the defibrillation process. Another common challenge for both automated and manual rhythm assessment is the occurrence of ECG artifacts during the resuscitation process which can adversely affect automated and manual rhythm assessment. ECG artifact may result from chest compressions, ambulance transport, or other patient motion. ECG artifact caused by patient motion can occur because when the patient's skin is stretched the voltage generated in or near the stratum granulosum can temporarily change by as much as a few millivolts. ECG artifact may also result from deformation of the electrode's metal-electrolyte interface, which can temporarily change the electrode's half-cell potential by as much as a few millivolts. ECG artifact may also result from movement of electrostatically charged rescuers near the patient or the defibrillator even when the patient is not touched. Electrostatically induced artifact occurs when a moving, electrostatically charged rescuer induces current flow through the ECG signal path. When the currents flow through the stratum corneum (top layer of the skin, which consists of dead skin cells) under each electrode, a differential voltage (sometimes exceeding twenty millivolts) can be generated at the input to the ECG amplifier.
While advanced medical device solutions exist for reducing electrical interference of ECG monitoring signals by the high level defibrillator charges and ECG artifact, defibrillator operators may benefit from improved electrical and ECG artifact solutions.